Since molybdenum (Mo) is a material having a low resistance value, that is, electrical resistance of 53.4 nΩ·m, it has superior electrical conductivity and thermal stability. Accordingly, molybdenum (Mo) is actively used for a back electrode of a copper indium gallium selenide (CIGS) solar cell.
A sputtering process is a film forming process using plasma to generate ions striking a sputtering target so as to stack a layer of atoms of the sputtering target on a substrate. The sputtering process is particularly used to generate a metal layer in various manufacturing processes in semiconductor and photoelectricity industries. Properties of the film formed during sputtering are related to intrinsic properties of the sputtering target, such as formation of a secondary phase having various crystal sizes and distributions. Accordingly, the sputtering target is regarded as an important factor in determining properties of a thin film.
Among existing solar cells, the CIGS solar cell has highest light absorbance coefficient (˜105 cm−1), a direct transition type band gap and heat stability to demonstrate little thermosetting property. Molybdenum (Mo) having good electrical conductivity and thermal stability is used for a back electrode of the CIGS solar cell.
A metal target manufacturing technology is largely divided into a dissolution/casting method and a powder metallurgy method. The dissolution/casting method is mostly widely used for forming a metal target because of various advantages, including facilitated mass production and reduced manufacturing costs.
However, since the dissolution/casting method has limitations in crystal particulate control and high density achievement, a multi-step process, including a rolling process, heat treatment, and so on, is required. In addition, according to the recent demand for a highly functional target material, many alloy targets are developed. However, the dissolution/casting method has a limitation in controlling a fine structure, making it difficult to form a target having uniform properties. On the other hand, the powder metallurgy method has several advantages, including uniform phase distribution and fine crystal particulate control, easy preparation of a material having high purity and a high melting point, a large degree of freedom in designing compositions and composition ratios, thereby manufacturing high performance, highly functional targets. Therefore, in recent years, the powder metallurgy method is actively used as a substitute for the dissolution/casting method.
In particular, since molybdenum has a high melting point of 2623° C., it is difficult to prepare molybdenum using the dissolution/casting method. Thus, it is often the case that molybdenum is prepared using the powder metallurgy method.
In the conventional powder metallurgy method for manufacturing a sputtering target, a hot isostatic pressing (HIP) method or a hot pressing (HP) method has been widely used, which can obtain a high-density sintered body by simultaneously applying temperature and pressure.
However, recently, for the following reasons: limitation in crystal particulate control due to a long molding process time, internal and external physical properties of a sintered body based on an external heating method, and high processing costs, and with the rapid advances in the IT industry, there is a demand for high performance, highly efficient sputtering target materials and development of new processing technologies is required.